This invention relates to a process for making a lithographic printing plate using an aluminum plate as a support and a processing solution to be used in the process, particularly to a process for making an aluminum lithographic printing plate using a silver complex salt diffusion transfer method and a processing solution to be used in the process.
Some examples of a lithographic printing plate using the silver complex diffusion transfer process (the DTR process) are described on pages 101 to 130 of Andre Rott and Edith Weyde, "Photographic Silver Halide Diffusion Processes", published by the Focal Press, London and New York (1972).
As described therein, there have been known two kinds of lithographic printing plates using the DTR process, i.e., a two sheet type in which a transfer material and an image-receiving material are separated and a mono-sheet type in which these materials are provided on one support. The two-sheet type lithographic printing plate is described in detail in Japanese Provisional Patent Publication No. 158844/1982. Also, the mono-sheet type one is described in detail in U.S. Pat. No. 3,728,114, Japanese Patent Publications No. 30562/1973 and No. 15765/1976, and Japanese Provisional Patent Publications No. 111103/1976 and No. 150105/1977.
The mono-sheet type lithographic printing plate utilizing the silver complex diffusion transfer process with the use of an aluminum plate as a support which is an object of the present invention (hereinafter referred to as "an aluminum lithographic printing plate") is described in detail in Japanese Provisional Patent Publication No. 118244/1982, No. 158844/1982, No. 26049:/1988, No. 116151/1991 and No. 282295/1992, and U.S. Pat. No. 4,567,131 and No. 5,427,889.
In the above-mentioned aluminum lithographic printing plate, physical development nuclei are carried on a roughened and anodized aluminum support and a silver halide emulsion layer is further provided thereon. A general process for making this lithographic printing plate comprises the steps of exposure, DTR development processing, water washing processing (washing off: removal of a silver halide emulsion layer with washing solution, hereinafter merely referred to as "washing processing") and finishing processing.
In detail, a metal silver image portion is formed on the physical development nuclei by the development processing and the silver halide emulsion layer is removed by the subsequent washing processing to expose the metal silver image portion (hereinafter referred to as "silver image portion"). Simultaneously, the anodized aluminum surface itself is exposed as a non-image portion.
On the exposed silver image portion and the non-image portion, a finishing solution containing a protective colloid such as gum arabic, dextrin, carboxymethyl cellulose, polystyrenesulfonic acid, etc. is coated for protecting the same. A processing of the so-called gum coating is applied to the surface of the plate. It is general that the finishing solution is called as a fixing solution and contains a compound which makes the silver image portion oleophilic (hereinafter referred to as "oleophilic agent").
As a problem in the process for making the above-mentioned aluminum lithographic printing plate, there is a problem of low ink receptivity at the silver image portion at initiation of printing. The ink receptivity is markedly lowered particularly by processing a large number of printing plates repeatedly for several days to several weeks which is so-called a running processing.
As a method for improving the ink receptivity, there is disclosed a finishing solution containing a protease and a hydrophobizing agent (an oleophilic agent) in U.S. Pat. No. 4,567,131, and a finishing solution containing a hydrophobizing agent (an oleophilic agent), a surfactant and a polyglycol in U.S. Pat. No. 5,518,866.
The ink receptivity is improved with a certain extent by the above-mentioned method, but lowering in ink receptivity in the running processing cannot sufficiently be improved.